Acoustic wave generating or receiving apparatus



H. c. HAYES 2,411,541

AQOUSjIIC WAVE GENERATING 0R RECEIVING APPARATUS Nov. 26, .1946.

Filed Aug. 8, 1936 mva'kron Harvey C. Hayes I ATTORNEY atentecl Nov. 26, 1946 ACOUSTIC WAVE GENERATING R RECEIVING APPARATUS Harvey C. Hayes, Washington, D. C.

19 Claims.

waves employed, to oscillate as a standing half wave in the direction of its thickness, that is, in the direction perpendicular to the face area. This determines the thickness of the disk or plate as a half wave lengthiixed by the velocityof the sound in the material of the plate at the frequency at which it is designed to operate. Much difficulty has been experienced in making the sound generating or receiving surface of the plate oscillate in phase and with uniform amplitude throughout its area. These difficulties are principally due to a lack of homogeneity of the plate and in particular to the radial expansion and contraction of the plate along the nodal plane caused by the changes of pressure therein resulting from the half wave standing wave system perpendicular to this nodal plane. These pressure changes tend to cause the plate to expand and contract along the nodal plane in accordance with Poissons ratio. Thus, there is a tendency to set up a radial standing wave system that reacts back along the half wave system to vary its amplitude across the plate. In

addition, and more seriously, a rim about a quar- Application August 8,1936, Serial No. 94,987

(Granted under the act of March 3, 1883, as

amended April 30, 1928; 370 0. G. 757) ter wave length 'wide about the plate or disk has a lower natural frequency than the rest of the plate because the Poisson expansion and contraction can take place here more readily than elsewhere since the unsupported boundary interposes no inertia against such expansion and contraction. As a result the restoring forces cooperative with the half wave system over this area become less and the natural frequency is lowered.

These undesirable features, namely, lack of uniformity of amplitude and a rim area having tion. However, it does not eliminate the dimculties arising from a lack of homogeneity in the material of the plate or head. Moreover, these vented heads are expensive to manufacture and give rise to difficulties when mounting the same ina housing by means of a flange, because the flange introduces restraints that interfere with the uniformity of amplitude and phase across the active face area.

With the foregoing preliminary discussion in view it is an object of my invention to provide an acoustical apparatus for generating and/or receiving sound wherein the sound generating or receiving surface vibrates substantially in eliminated or reduced to a negligible minimum.

It is a further object of my invention to provide an acoustical apparatus for generating and/or receiving sound which is simple in construction and is susceptible of being economically manufactured and wherein the noted 'd eficiencies of non-uniformity of amplitude of vibration-and out of phase vibration of the sound generating or receiving surface are substantially eliminated or reduced to a negligible minimum.

It is another and further object of my invention to provide a substantially homogeneous vibratory body or mechanism of high acoustical efllciency for generating and/or receiving sound wherein the noted deficiencies of non-uniformity of amplitude of vibration and out of phase vibration of the sound generating or receiving surface.

are substantially eliminated or reduced to a negligible minimum.

These and other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following description when considered in connection with the accompanying drawing wherein:

Fig. 1 shows a perspective view in partial section of one embodiment of my invention which is particularly adapted for use in cases wherein the directivity is horizontal;

Fig. 2 shows a perspective view in partial section of another embodiment of my invention which "be used for either horizontally or vertically directive work;

Fig. 3 is a partial sectional view of a still further embodiment of my invention which may be used for either horizontally or vertically directive work;

Fig. 4 is a partial sectional view of still another embodiment of my invention which is designed to facilitate in phase vibration.

Turning now to Fig. l of the drawing there is shown'depicted therein a metal disk I having a plurality of recesses 2. The bottom portion of each of the recesses is closed by the metal of the disk at 3 and serves as a diaphragm to which any means may be secured for imparting vibratory energy to and/or receiving vibratory energy from a substantial homogeneou body supported thereby. As illustrative of the means secured to the diaphragm 3 I have shown in the drawing a magnetostrictive element or electro-mechanical energy interchanging means l, it being apparent to those skilled in the art, however, that I may employ a piezo-electrical means if desired. The diaphragm 3 with its attached electro-mechani- 1 cal energy interchanging means d is preferably tuned to substantially the same natural mechanical frequency as the element or body supported in the recess above the diaphragm. In use this vibratory body faces with its apertures directly into the medium of propagation with the result "that the apertures are filled with the medium whereby to provide a plurality of substantially homogeneous vibratory elements. It is at once obvious that the device of Fig. 1 as well as the devices of my other embodiments may be used fortransmitting and/or receiving sound.

, However, the arrangement of Fig. 1 cannot be used for depth sounding where the plate must face vertically downward thru an opening in the ship's envelope because the recesses are filled up in part or in whole with air When installed and there are no means for escape during the vessel's passage thru the fluid medium. For such purposes the apertured plate is positioned within a housing having a sound transparent window directly in front of the recesses. The housing is pumped free of air and filled with a fluid medium such as castor oil or other liquid, having an acoustical impedance or property substantially equal to that of the fluid medium contacting the exterior of the sound transparent window. By the words sound transparent is meant that the sound waves incident upon the material of the window are neither appreciably reflected nor absorbed, this desideratum being attained when the acoustical properties of the window material are substantially equal to those of the fluid medium in contact therewith. The acoustical properties or impedances of two substances are alike or different depending upon whether the products of the density and the velocity of sound in them are alike or different.

In Fig. 2 of the drawing is shown an embodie ment of my invention ceding paragraph wherein 5 indicates the sound transparent window forming a part of the housmg 6; 1' designates the fluid medium within the housing, such as castor oil or other liquid, having an acoustical impedance substantially equal to that of the fluid medium in contact with the window exterior; and 8 the vibratory body or mechanism which is identical with that disclosed in Fig. 1 of the drawing. The vibratory mechanism 8 is secured to the'closure member 9 of the housing by means of the flange Ill projecting there-- from and the fluid impervious lining ll so as to insure that the fluid medium 1 within the housas described in the preing will be free from contact with the rear of the vibratory body 8 and the electro-mechanical energy interchanging means i2 secured thereto. This mounting prevents the fluid medium 1 from contacting the rear of the plate and the means secured thereto and hence avoids any damping of their free motion. While I have shown a specific type of mounting for the vibratory body or mechanism 8 within the housing I5, I do not desire to be limited thereto since any mounting will serve the purpose so long as the recessed plate or body 8 is positioned to prevent the fluid medium within the housing from contacting therear thereof and the electro-mechanical energy interchanging means secured thereto.

In Fig. 3 is shown an embodiment of my invention which is similar to that of Fig. 1 except that the recesses are filled with a compound having an acoustical impedance substantially equal to that of the fluid medium which it is adapted to contact. While many compounds will readily sugeest themselves to those skilled in the art, I have found that certain rubber compounds may be conveniently used for this purpose. The general types of soft vulcanized rubber, for example, when immersed in water or in another liquid having similar acoustical properties, will transmit compressional,longitudinal sound waves, the degree of transmission varying considerably with the compound used. The closer the acoustical impedance of the compound matches that of the medium in which it is immersed, the more elliciently it will act as a propa'gational medium. Any one familiar with the physical properties required for sound'transmission and versed in the art of compounding and processing elastic,-

resilie'nt insulating substances will readily perceive the many compounds which can be made from rubber alone.

The rubber compound I3 is vulcanized to the walls of the cylinder and to the bottom enclosing diaphragm. It resonates within the cylinders quite similarly to water or other liquid and keeps the space free from air bubbles even when faced downward for depth finding.

Fig. 4 shows an embodiment of my invention which is similar to that of Fig. 1 with the exception that adjacent cylinders are interconnected by a small passageway or perforation which is preferably at the nodal plane as shown at H or may be otherwise placed at l5, for example, adjacent the diaphragm. These perforations or passageways H or ii serve as a coupling between the several resonated columns orvibratory elements and facilitate their oscillating in like phase. Theembodiment in Figs. 2 and 3 may also be provided withthese passageways or perforations if desired. It is to be emphasized however, that these passageways or perforations are not absolutely essential since the various embodiments operate satisfactorily without them, particularly when slightly detuned. These perforations or passageways should be kept as short as possible. I prefer that their length should be less than a quarter wavelength, which wavelength is fixed by the velocity of sound in the material of the vibratory elements at the frequency for which the device is designed to operate. If the perforations or passageways connecting adjacent columns or elements are'longerthan this there is too much phase change thru the coupling to enable the coupling to keep adjacent columns or elements in phase. Moreover, if the adjacent columns are separated more than a quarter wavein the material filling the recesses of the disk and at the frequency for which the device is designed to operate, the combined output from all will not give a plane wave front, but a spotted wave front, and the required directivity or focusing effect will be lessened.

Regarding the length of the plate recesses or elements therein, their diameter and relative spacing, the following may be said; I prefer that the depth or length of the recesses be definitely made alike and substantially equal to some whole number of quarter wavelengths fixed by the velocity of the sound or vibration in the material filling the recesses and at the frequency for which the device is designed to operate. It is also preferred that the diametercof each of the vibratory columns or elements filling each of the recesses and the distances between the centers of each pair of adjacent vibratory columns or elements be not greater than a half wavelength determined by the velocity of the vibration in the'material filling said recesses and the frequency for which the vibratory mechanism is designed.

The metal of the apertured plate or disk in all of my embodiments is preferably a metal having a small temperature co-efficient of elasticity and low internal losses attendant upon its being mechanically oscillated at relatively large amplitudes. Invar, phosphor bronze and aluminum possess the recited preferred characteristics but other metals which will serve the purpose equally well will readily suggest themselves to those skilled in the art.

According to the provisions of the patent statutes I have-set forth the principle and mode of operation of my invention and have illustrated and described what I now consider to represent its best embodiments. However, I desire to have it understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically illustrated and described.

The invention herein described may be manufactured and used by or for the Government of the United States of America for governmental purposes, without the payment of any royalties thereon or therefor.

- I claim:

1. A vibratory body comprising in combination a plate having a plurality of recesses and a substantially homogeneous material filling each of said recesses whereby to provide a. plurality of vibratory, substantially homogeneous elements. said material having an acoustical impedance substantially equal to that of the medium of propagation with which the vibratory body is to be used, and individual means for driving each of said vibratory elements.

2. A vibratory body comprising in combination a plate having a plurality of recesses and a substantially homogeneous material filling each of said recesses whereby to provide a plurality of vibratory, substantially homogeneous elements, the material filling said recesses being that of the medium of propagation with which the vibratory body is to be used, and individual means for driving each of said vibratory elements.

3. A vibratory body comprising in combination a plate having a plurality of recesses and a substantially homogeneous material filling each of said recesses whereby to provide a. plurality of vibratory, substantially homogeneous elements, means for coupling said vibratory elements to facilitate in-phase vibration of the same, and individual means for imparting vibratory energy to each of said vibratory elements.

4. A vibratory mechanism comprising in combination a plate having a plurality of recesses, a substantially homogeneous material filling each of said recesses whereby to provide a plurality of vibratory, substantially homogeneous elements and individual means for imparting or. receiving vibratory energy respectively to or from each of said vibratory elements substantially along the longitudinal axis thereof.

5. A vibratory mechanism comprising in combination a plate having a plurality of recesses, a substantially homogeneous material filling each of said recesses whereby to provide a plurality of vibratory, substantially homogeneous elements and individual means for imparting or receiving vibratory energy respectively to or from each of said vibratory elements substantially along the longitudinal axis thereof, said material having an acoustical impedance substantially equal-to that of the medium of propagation with which the vibratory mechanism is to be used.

6. A vibratory mechanism comprising in .combination a plate having a plurality of recesses, a substantially homogeneous material filling each of said recesses whereby to provide a plurality of vibratory, substantially homogeneous elements, individual means for imparting or receiving vibratory energy respectively to or from each of said vibratory elements substantially along the longitudinal axis thereof, and means for coupling said vibratory elements to facilitate in-phase vibration of the same.

'7. A vibratory mechanism comprising in combination a plate having a, plurality of recesses, a substantially homogeneous material filling each of said recesses whereby to provide a plurality of vibratory, substantially homogeneous elements and individual similar means for imparting vibratory energy .to each of said vibrating elements or receiving vibratory energy therefrom, the wall common to each pair of adjacent recesses bein perforated and the material within said recesses extending into the perforations thus formed whereby to couple said vibratory elements and to facilitate in-phase vibration of the same.

8. A vibratory mechanism comprising in combination a plate having a plurality of recesses, a substantially homogeneous material filling each of said recesses whereby to provide a plurality of vibratory, substantially homogeneous elements and individual similar means'for imparting vibratory energy to each of said vibratory elements or receiving vibratory energy therefrom, the wall common to each pair of adjacent recesses being perforated and the material within said recesses extending into the perforations thus formed whereby to couple said vibratory elements and to facilitate in-phase vibration of the same and the length of each perforation being less than a quarter wave length Which wave length is fixed by the velocity of the vibration in the material filling said recesses and the frequency for which the vibratory mechanism is designed.

9. A vibratory mechanism comprising in combination a plate having a plurality of recesses, a substantially homogeneous material filling each of said recesses whereby to provide a plurality of vibratory, substantially homogeneous elements and individual similar means for imparting vibratory energy to each of said vibratory elements or receiving vibratory energy therefrom, the depth of each recess being substantially equal to a whole number of quarter wave lengths, which Wave length is fixed by the velocity of the vibration in the material filling said recesses and the frequency for which the vibratory mechanism is designed.

10. A vibratory mechanism comprising in combination a plate having a plurality of recesses, a substantially homogeneous material filling each of said recesses whereby ito provide a plurality of vibratory, substantially homogeneous elements and individual similar means for imparting vi-, bratory energy to each of said vibratory elements or receiving vibratory energy therefrom, the diameter of each of said vibratory elements being no greater than a half wave length which wave length is fixed by the velocity of the vibration in the material filling said recesses and the frequency for which the vibratory mechanism is designed.

11. A vibratory mechanism comprising in combination a plate having a plurality of recesses, a substantially homogeneous material filling each of said recesses whereby to provide a plurality of vibratory, substantially homogeneous elements and individual similar means for imparting vibratory energy to each of said vibratory elements or receiving vibratory energy therefrom, the distance between centers of each pair of adjacent vibratory elements beingno greater than a half wave length which wave length is fixed by the velocity of the vibration in the material filling said recesses and the frequency for which the vibratory mechanism is designed.

12. A vibratory mechanism comprising in combination a plate having a plurality of recesses,

asubstantially homogeneous material filling each of said recesses whereby to provide a plurality of vibratory, substantially homogeneous elements and individual similar means for imparting vibratory energy to each of said vibratory elements or receiving vibratory energy therefrom, the length of each vibratory element being substantially equal to a whole number of quarter wave lengths and the diameter of each of said vibratory elements and the distance between centers of each pair of adjacent vibratory elements being no greater than a half wave length, all of said wave lengths being fixed by the velocity of the vibration in the material-filling said recesses and the frequency for which the vibratory mechanism is designed.

13. A vibratory mechanism comprising in combination a plate having a plurality of recesses, a substantially homogeneous material filling each of said recesses whereby to provide a plurality of vibratory substantially homogeneous elements and individual electro-mechanical energy interchanging means connected to each of said vibratory elements.

14. A vibratory mechanism comprising in combination a plate having a plurality of recesses, each of which is provided at one end with a closure member, a substantially homogeneous material filling each of said recesses whereby to provide a plurality of vibratory, substantially homogeneous elements, and electro-mechanical energy interchanging means connected to each oi said closure members.

15. A vibratory mechanismoomprising in combinat-ion a plate having a plurality of recesses,

each of which is provided at one end with a closure member, a substantially homogeneous material filling each of said recesses whereby to provide a plurality of vibratory, substantially homogeneous elements, and electro-mechanical energy interchanging means connected to each of said closure members, each closure member and its associated electro-mechanical energy interchanging means together having substantially the same natural mechanical frequency as the vibratory element adjacent thereto.

16. An acoustical apparatus comprising in combination a fluid impervious housing having a portion thereof which is sound transparent, a substantially homogeneous fiuid medium within said housing of an acoustical impedance substantially equal to that of the fluid medium contacting the housing exterior, a plate positioned within said housing adjacent the sound transparent portion thereof and having a plurality of recesses filled with the aforementioned substantially homogeneous fluid medium whereby to provide a plurality of vibratory substantially homogeneous elements, and individual means for imparting or receiving vibratory energy respectively to or from each of said vibratory elements.

17. An acoustical apparatus comprising in combination a fluid impervious housing having a portion thereof which is sound transparent, a substantially homogeneous fluid medium within said housing of an acoustical impedance substantially equal to that of the fluid medium contacting the housing exterior, a plate positioned within said housing adjacent the sound transparent portion thereof and having a plurality of recesses filled with the aforementioned substantially homogeneous fluid medium whereby to provide a plurality of vibratory substantially homogeneous elements, and individual electro-mechanical energy interchanging means for imparting or receiving vibratory energy respectively to and from each of said vibratory elements.

18. A vibratory body comprising in combination a plate having a plurality of recesses and a substantially homogeneous material filling each of said recesses whereby to provide a plurality of vibratory, substantially homogeneous elements, the wall common to each pair of adjacent recesses being perforated and the material within said recesses extending into the perforations thus formed whereby to couple said vibratory elements and to facilitate in-phase vibration of the same, and means for imparting vibratory energy to each of said vibratory elements or for receiving vibratory energy therefrom.

19. A vibratory body comprising in combination a plate having a plurality of recesses and a substantially homogeneous material filling each of said recesses whereby to provide a plurality of vibratory, substantially homogeneous elements, the material filling said recesses being a rubber compound having an acoustical impedance sub-- stantially equal to that of the medium of propagation with which the vibratory'body is to be used, and means for imparting vibratory energy to each of said vibratory elements or for receiving vibratory energy therefrom.

HARVEY C. HAYES. 

